Air quality in Denver was badly affected by wildfire smoke from blazes in Oregon and provinces of western Canada on July 24, 2024.
David Zalubowski/AP
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David Zalubowski/AP
Wildfire season is here again, and where there’s fire, there’s smoke – which, research shows, can be as deadly as the flames themselves.
Recently, a group of scientists sought to quantify the long-term outcomes of smoke exposure from California wildfires between 2008 and 2018. Their paper modeled statewide levels of tiny particles in wildfire smoke called PM2.5, and applied mortality data by ZIP code. They estimated that up to 55,710 premature deaths were attributable to wildfire-related PM2.5 in the air.
Around 90% of wildfire smoke is made up of these particles, which are 30 times smaller than the diameter of a strand of hair. “PM2.5 particles can migrate deep into the lungs, and, from there, into the bloodstream, causing everything from inflammation to asthma attacks to sudden cardiac death,” says Mary Johnson, a research scientist at the Harvard T.H. Chan School of Public Health, who studies the health impacts of wildfires.
While the premature death study looked at California, smoke from megafires can waft thousands of miles, putting people who aren’t as aware of its risks in harm’s way. “If you’re in California or Texas, you’re used to closing windows, staying inside, and turning on an air purifier when there’s a wildfire,” says Johnson. But as climate change makes large fires more frequent, everyone needs to be prepared to protect themselves.
And people with certain health conditions face increased risks. Here’s what to know – with specific guidance for high-risk groups.
Basic precautions: Watch for high AQI
If you hear about wildfires in the news, or if the sky looks hazy, check the Air Quality Index at AirNow.gov or PurpleAir.com. If the AQI is above 100, avoid outdoor exercise. If it’s above 150, wear a tight-fitting N95 mask when you’re outside. Run your air conditioner with a high-efficiency filter installed – the EPA recommends MERV 13 or above – or use a portable HEPA air purifier. (The EPA provides instructions for making your own HEPA air cleaner with a box fan, here.)
For high-risk groups
If you’re in one of the following high-risk groups, consider taking additional steps. Some experts advise setting up a designated “clean room,” with few windows and doors and its own portable HEPA air cleaner. It’s a good idea to avoid things that add to indoor air pollution, like vacuuming, lighting candles, or using a gas stove and to repair drafty windows and doors. If air quality is bad, time your outdoor activity for times of day with lower AQI readings; and ask your doctor what you should do to protect yourself. If it’s feasible, leave the area for somewhere outside the smoke zone.
If you’re pregnant
“Pregnancy increases your respiratory rate, so you’re inhaling more smoke,” says Dr. Amy Padula, associate professor in the department of obstetrics and gynecology and reproductive sciences at the University of California at San Francisco. “PM2.5 gets into the bloodstream and reaches the placenta, where it may affect the fetus.”
In a study published earlier this year, she and her colleagues found that exposure to PM2.5 from wildfire smoke during pregnancy was associated with higher odds of giving birth prematurely. Babies born early are more likely to have immature lungs and developmental delays. They’re also more likely to die in their first year.
Bottom line: If the AQI is above 100, stay inside as much as possible, with windows and doors closed, and wear a NIOSH approved N95 respirator outside.
For children
“Kids get a higher dose of PM2.5, because they’re active and they breathe more air relative to their weight – both of which are hard on underdeveloped lungs,” says Dr. Lisa Patel, a member of the American Academy of Pediatric Council on Environmental Health and Climate Change. “Lungs grow quickly from birth to age five and keep developing through the early 20s. Early exposure to wildfire smoke leads to the formation of asthma. It can also exacerbate asthma and cause pneumonia in kids.”
A 2021 study revealed that wildfire-related PM2.5 is ten times more harmful to children’s respiratory health than PM2.5 from other sources, like air pollution. Exposure to the tiny particles is also linked to increased risk of ADHD, autism, and poor school performance.
Bottom line: “We need child-specific wildfire smoke guidance,” says Dr. Patel, who has young children. In its absence, it makes sense to err on the side of caution with very young children and those with asthma or who are particularly sensitive. In her own family, Dr. Patel says, “when the AQI is above 50, we spend more time indoors with the air filter on. If it’s above 100, we don’t go outside.” Especially if the air is smoky for more than a few days, it’s good to reduce outdoor time, according to advice from Mount Sinai’s Icahn School of Medicine.
If your child has asthma, make sure you have medication on hand and stay in close contact with your pediatrician, Patel adds.
Adults with asthma and COPD
“Chronic lung conditions are caused in part by airway inflammation. Wildfire smoke induces inflammation, so it exacerbates those conditions,” explains Dr. John Balmes, a pulmonologist and professor emeritus of environmental health sciences at the University of California at Berkeley. A number of studies have found that people with asthma and COPD are more likely to visit the ER or be hospitalized after wildfire smoke exposure.
Some people also experience longer-lasting decreases in lung function. When researchers looked at data from patients at a North Carolina allergy clinic, they found decreases in peak respiratory flow one year after two separate fires had affected the area.
Bottom line: Because N95 masks can make it more difficult to breathe, opt for one with an exhalation valve, suggests Balmes. In addition to staying inside if the AQI is higher than 100, monitor your breathing with a peak flow meter. If you’re in the red zone and have taken your rescue bronchodilator medication, go to urgent care or the ER, says Balmes. If you’re checking your oxygen saturation with a pulse oximeter, go to the ER if it’s 84% or lower. (Beware: they don’t work as well on darker skin tones.)
If you’re over 65: Watch for lung and cardiovascular risks
“Older people are more likely to have high blood pressure, heart problems, and other conditions that make them more vulnerable to the toxic effects of wildfire smoke,” says Harvard’s Johnson. A study published in the Journal of the American Heart Association in 2018 found that people over 65 were more likely to go to the ER with a range of cardiovascular problems, like heart attack, dysrhythmia, pulmonary embolism, and stroke, on or after dense smoke days. Research suggests that older women and Black people may be particularly susceptible to respiratory problems when exposed to wildfire smoke.
Bottom line: If you have heart or lung problems, ask a neighbor to pick up your mail, take out your trash, or run errands for you when the AQI is above 150, and if you have to go outside, wear a tight-fitting N95 mask, says Balmes.
If you work outdoors
Farm workers. Construction crews. Bike messengers. Landscapers. Millions of people have outdoor jobs – and don’t get time off for smoky air. The work is often strenuous, which means they’re inhaling more PM2.5. While there’s little research assessing the effects on outdoor workers’ health, it’s safe to assume regular exposure to unhealthy air takes a toll. The Occupational Safety and Health Administration’s says federal law entitles you to a safe workplace, and workers have a right to speak up about hazards or refuse to work in a hazardous situation.
The Centers for Disease Control suggests all employers relocate or reschedule work tasks to less smoky areas or times of day and encourage workers to take frequent breaks. Oregon, California, and Washington are the only states that have adopted rules for employers to limit employees’ exposure, including providing N95 masks to workers. But compliance, according to a 2021 investigation in California by KQED and the California Newsroom, is spotty at best.
Bottom line: Wear an N95 mask with an exhalation valve when you’re outside in smoky air, even if your employer doesn’t provide one.
Household pets
“If you’re feeling the impact of smoke, your pet is, too,” says Lori Teller, a veterinarian and a clinical professor at Texas A&M University College of Veterinary Science. “Coughing and gagging are signs they’re affected. Wildfire smoke can injure their lungs and, when the particles get in the bloodstream, cause damage to other organs.” Birds are extremely sensitive to smoke, because they take in almost double the amount of oxygen with each breath as mammals. Brachycephalic breeds, like French bulldogs, pugs, and Persian cats, have compacted respiratory tracts and may be more impacted by smoke, too.
Bottom line: If the AQI is over 100, it can be dangerous for puppies and kittens, senior animals and those with heart or lung problems. If it’s over 150, keep pets inside apart from quick bathroom breaks for dogs, and “entertain them by playing fetch in the hallway or teaching them new tricks,” says Dr. Teller. “If your pet is having trouble breathing and its eyes are red and watery, call your vet. It might need oxygen supplementation.”
Ginny Graves is a freelance journalist in the San Francisco Bay Area focused on science, health and psychology.
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